Aspects of the present disclosure relates to performance and safely characterization or assessment systems and processes. In particular embodiments of the disclosure are directed to apparatus and methods for safety and performance characterization capable of operating before, during, and after a destructive event from a system or item under test.
Calorimetry can include processes of measuring an amount of heat released or absorbed during a chemical reaction. Calorimetry can be used in a wide range of material analysis across multiple industries. An Accelerating Rate Calorimeter (ARC) method is one method used where a material sample is placed within an oven type enclosure. Temperature within the enclosure is elevated through multiple step increases with rest periods at each step. This increase continues until the sample reaches a thermal runaway condition where the heat release of the sample can be recorded.
For battery characterization, the ARC methodology is questionable as the increasing heat may not be representative of real world conditions and may impact data collection. Lithium battery heat generation, as it approaches thermal runaway, is of interest as well as what occurs during the event.
A new approach can include use of isothermal calorimetry methodology where the cell's ambient temperature is controlled tightly during actual testing. This exemplary approach allows tor an accurate evaluation of heat generated from chemical reactions or physical changes occurring within the cell. A goal can include use of various embodiments of the disclosure to evaluate isothermal calorimetry as a potential method for characterizing the potential energy release during a destructive event, the impact to surrounding environment, and risk mitigation development.
According to an illustrative embodiment of the present disclosure, embodiments of the disclosure include exemplary processes and associated equipment to adapt or construct a heat flow calorimeter to accept a scaled pressure vessel. In some embodiments, an apparatus is provided that combines a robust sample environment of a closed bomb (to enable overcharge, burn, detonation, etc. of any sample in the closed bomb) with a highly sensitive detection capability including heat flow calorimetry. In particular, some embodiments have been constructed containing a pressure vessel in a sample chamber of the calorimeter for sample materials that would then be forced fully through decomposition. In some embodiments, an exemplary system included a pressure vessel and a capacity for deliberate overcharging of Lithium containing batteries in order to determine resulting pressure and heat energy released.
Also, efforts to obtain increased energy density of battery cells highlight a need for electrochemical techniques as well as additional characterization methods for these cells in order to meet user needs and safety requirements. In particular, a continuing need has called forth inventive efforts for developing novel calorimeters to satisfy various requirements for requiring activities including high energy density systems such as chemical energy storage systems, propellant, explosive, and pyrotechnic devices. To support optimization of electrochemical energy storage systems in particular it is necessary to understand their thermal characteristics at rest and under prescribed charge and discharge cycles. In one example, a need existed to develop a calorimeter system able to accommodate multiple battery cell configurations and provide empirical system data for use in modeling and simulation. The performance benefits from Lithium batteries are tempered by specific drawbacks, such as cost and safety being the major concerns. Lithium batteries or individual cells can experience violent behavior when subjected to abusive conditions or design flaws that can cause a destructive event. Overcharge, short circuit, and high environment temperature are just some of the conditions that can cause such events. During an event, cells can exhibit such characteristics as extreme high temperatures, deflagration, fire, and venting of electrolyte and/or toxic materials. The cell's characteristics prior to, during, and after a destructive event is important in developing preventive and mitigating hazard steps. To further understand the worst-case event produced by electrochemical cells a novel measuring system based on isothermal bomb calorimetry was developed. This system allowed for the containment of the reaction and its products while measuring the pressure and release rate of the gaseous product, as well as a complete thermal profile of the reaction. Heat flows from 0.01 to 195.42 Watts were measured with an average signal noise less than 1 mW. Moreover, these needs also included a requirement to create testing systems which are capable of larger testing capabilities that necessarily include a need to use larger systems, create more testing options with respect to samples under test, and create an ability to more cost effectively repair or replace costly components in such test systems which existing systems do not accommodate in a cost or time effective manner. As systems are scaled up in size, there is a higher level of failures in system components which require new designs to accommodate repairs or maintenance rather than throwing out large sub-assemblies. Also, there is a need to be able to swap out components for greater customized design or configurability of testing systems with respect to desired testing processes or data collection.
As an example of one embodiment, an improved measuring cell was designed and constructed to measure the heat flow of larger cells (e.g., 38 Ahr). Heat flows from 0.01 to 195.42 Watts were measured with an average signal noise less than 1 mW. This embodiment was also designed to eliminate the restrictions imposed by the stable temperature bath. By replacing the bath with a heat exchanging assembly, cost is reduced while the limits on sample size and orientation are eliminated.
Embodiments of the disclosure can include apparatus and methods for providing flexible and repairable testing capabilities for systems that generate or absorb heat such as energy storage systems. One embodiment can include a stable temperature heat exchanging assembly adapted to contain and maintain a thermally conductive fluid at a predetermined temperature, heat sinks, thermal sensor assemblies, an internal containment structure, and thermal barriers between different elements of the disclosure to isolate different sections from each other. An embodiment of the disclosure can include a system where the thermal sensor assemblies and heat sinks removeably attach to different sections of the inner containment structure so as to measure heat flow into or out of the inner containment structure's different sections without being altered by direct thermal contact with other inner containment sections. Embodiments of the disclosure permits rapid insertion/removal of samples as well as replacement of sections of an exemplary system including embodiments or parts of the thermal sensor assemblies as well as providing an ability to obtain separate thermal measurements associated with different sections of a sample under test within the inner containment structure. Other aspects of the disclosure include a capability to insert or substitute existing components such as containment structure elements, thermal sensors etc. with different sized elements or structures to accommodate different types of samples or differently sized samples under test. Embodiments can include electrical bus or wiring structures such as separate wiring sections and quick disconnects that also permit rapid repairs or alteration of configurations of various aspects of embodiments of the disclosure.
Existing systems do not provide a needed capability in a variety of areas including chemical battery testing. For example, existing systems might provide the closed bomb and low sensitivity or alternatively heat flow sensitivity but much stricter sample environment but not a combination thereof.
Additionally, existing systems are bulky, heavy, and have limited portability creating problems for ease of use. Exemplary embodiments of the present disclosure are lightweight and implement a mobile platform system to increase mobility and portability of the disclosure.
Additional features and advantages of the present disclosure will become apparent to those skilled in the art upon consideration of the following detailed description of the illustrative embodiment exemplifying the best mode of carrying out the disclosure as presently perceived.